car runs too cool...SOMETIMES

[R.O.R-2.0]

ok boys and girls.. my rabbit is having problems staying up to temp.

whenever i coast down a long hill, the engine comes down from operating temp. it usually sits at about the 5th mark on the temp gauge. when i coast for a ways, it will go down past the first mark, and get close to where the gauge needle rests when its cold.

am i on the right track thinking that my thermostat is sticking open?

motorad brand 180* (82*c) thermostat. no idea how old it is.

heater gets about luke-warm when it does this.

its always dropped like 1 line on the gauge going down long hills, but never almost all the way to the cold peg. and now it wont stay up to temp going 55 down the road. it was like 47* yesterday.. 

[maxfax]

Sounds like a t-stat to me..  Make sure the housings aren't corroded around that area...

[theman53]

My T stat always acts weird when it goes from cold outside to hot and back. It does it a couple of days and then seems to act normal again.

[VWCaddy]

IS it the fail safe version of the Motorad t-stat?  I had one on my Toyota that got hot enough once to lock it open (with the fail safe feature) and it was that low heater output and low operating temp that clued me into checking the t-stat (and yes it was locked open).

[erice1984]

Only a few things.

Low on coolant? (not likely)

Water pump leaking? (water pump no circulating enough) (not likely)

Thermostat stuck open. (likely)

Radiator cap not holding pressure,  coolant boiling. (not as likely)


I put money on thermostat, get a 90*C/195*F t-stat, give your engine the highest temp to get hot.

[coke]

I think my thermostat is sticking open too. Really makes me angry because I checked it 4 times before I put it in the engine, and now I have to remove my power steering bracket again and the coolant flange and all that junk and put more coolant in it. Grr.

I can watch my temperature gauge go down when its up to temperature (if it ever gets that far) when I turn the blower fan on full speed.

[R.O.R-2.0]

Sounds like a t-stat to me..  Make sure the housings aren't corroded around that area...

housings not corroded.. but the bottom water neck now has a drain plug.. i was so excited when i saw the drain plug thread..

[R.O.R-2.0]

IS it the fail safe version of the Motorad t-stat?  I had one on my Toyota that got hot enough once to lock it open (with the fail safe feature) and it was that low heater output and low operating temp that clued me into checking the t-stat (and yes it was locked open).

no idea.. took my thermo out yesterday, boiled it, and it opens a tad before 190, and is fully open at a tad over 200*

i drilled a small vent hole in it before i re-installed it too.

and just so we are clear, this is the thermostat that i bought my car with..

[8v-of-fury]

If your engine is loosing heat off load, and your thermo opens and then therefore must close at around 190.. I lean towards the cold air coming in through the front and physically cooling the motor as it passes by it and out through the bottom. Piece of cardboard in front of your rad, with the half that the hoses go in (passenger side) uncovered. Try it out.

[R.O.R-2.0]

If your engine is loosing heat off load, and your thermo opens and then therefore must close at around 190.. I lean towards the cold air coming in through the front and physically cooling the motor as it passes by it and out through the bottom. Piece of cardboard in front of your rad, with the half that the hoses go in (passenger side) uncovered. Try it out.

dont you think it woulda done it way worse when it was frigid (low 20's) and not now, when its in the mid 40s?

like i say, its always done this A LITTLE BIT (move down one mark on the gauge) but now it almost goes back down to where it would be if the engine were just started..

i doubt my 45* air is cooling my engine down that far..

[8v-of-fury]

Alright, then whats wrong with it

Its not over heating, so the pump is circulating. Thermostat works correctly. No corrosion in the housings.

Upon thinking it over one of two, or both things have happened. You need a new temp sensor, or temp gauge. Its either not giving the correct resistance, or not seeing the correct resistance. Sounds plausible eh!

And yes on a diesel coasting downhill should remove a ton of heat, as your are producing practically ZERO while coasting.. other than that created by friction of the pistons and cylinders..

How does it run.

[R.O.R-2.0]

Alright, then whats wrong with it

Its not over heating, so the pump is circulating. Thermostat works correctly. No corrosion in the housings.

Upon thinking it over one of two, or both things have happened. You need a new temp sensor, or temp gauge. Its either not giving the correct resistance, or not seeing the correct resistance. Sounds plausible eh!

And yes on a diesel coasting downhill should remove a ton of heat, as your are producing practically ZERO while coasting.. other than that created by friction of the pistons and cylinders..

How does it run.

runs great. has power, still makes heat, but you can feel it in the heater when it starts coming down from operating temp. the heater gets luke-warm.

and yes, im aware these cars inject no fuel while coasting.. hard to build heat with no fire..

i kinda thought about it being a bad sender, but i kinda doubt it now. if it were constant/predictable, i would think maybe it were the gauge or sender. but its soo sporadic that im thinkin the thermo is just sticking open occasionally..

[maxfax]

I'm guessing the luke-warm heat symptom came at the same point the temp dropping started which means indeed it's cooling down..  But, old electric factory gauges (put there as merely a suggestion of what's going on) can do all sorts of things too..   From my experience, constant and predictable is not the more common symptom of a gauge problem..  I have an aftermarket mech gauge taking a reading from the same housing as the factory gauge...  They rarely coincide...

  The last thermostat in my car was a screwball for sure..  Engine ran hotter in colder ambient temps..     It wasn't a bad thing at least.. Maybe it was from being well lubed from all the oil in there...

[Bugsy_malone 666]

Get a genuine VW thermostat. Thermostats tend to not be massively expensive and its one thing for piece of mind if you have a genuine article in there.

I am pretty sure it should be the type that opens at 86deg C.

My mk3 golf had issues with warm up and on the motorways it would barely get above the 5th little marker at the bottom of the gauge (basically the warm up bit or white bar depending on your gauge). I changed the thermostat and it warms up to 70deg C on motorway cruises and only round town does it get to 90(the middle). my mk6 tdi runs at 90c all day long, they are designed to run at that temperature for optimum performance/economy.

I always change the thermostat if its a different engine I am installing and havent changed it before, almost like changing the oil filter/fuel filter.

[R.O.R-2.0]

only way to get a genuine VW thermostat around here is to get raped by the VW service shop..and none of those guys know SQUAT..